The Magoffin marine unit is a Middle Pennsylvanian age interval
of marine strata that directly overlies the Taylor, Copeland,
and correlative coal zones in the Appalachian basin. For this
study the Magoffin was measured, described, and sampled at 17
localities along a northeast to southwest transect in the center
of the Middle Pennsylvanian outcrop belt in eastern Kentucky and
West Virginia. Throughout the study area the base of the Magoffin
is characterized by a thin, dark, highly fossiliferous limestone
with a brachiopod-dominated fossil assemblage. The limestone base
is usually overlain by a fining-upward sequence consisting of
fossiliferous dark shales or mudstones with mollusk-dominated
assemblages. These dark mudstones include a fissile black shale
with a distinctive Posidonia fauna deposited over part of the study area. The lower, fining
sequence is overlain by a thicker, coarsening sequence bearing
brachiopod-dominated fossil assemblages. The lower beds of the
Magoffin, particularly the basal limestone, are persistent and
relatively uniform throughout the study area. In contrast, strata
in the upper part of the Magoffin sequence show a high degree
of geographic variability, with localities in the southwestern
half of the study area showing two successive, thick, coarsening-upward
sequences of strata, while those to the northeast record a single
thinner coarsening-upward sequence. The widespread, uniform nature
of the basal Magoffin limestone appears to indicate rapid transgressive
flooding of the coal-swamp and associated environments accompanied
by a hiatus in clastic influx into the Magoffin seaway. Nearshore
brachiopod faunas were replaced by deeper-water, possibly dysaerobic-adapted
mollusk faunas as transgression progressed, culminating in the
fissile black shales and monotaxic Posidonia fauna deposited beneath a localized pycnocline during maximum
transgression. The onset of regression is indicated by the reverse
of the stratigraphic sequence of faunas observed during transgression,
and by the return of rapid clastic influx into the basin.